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Feromagnetic "π"-junctions

T. Kontos, M. Aprili, J. Lesueur, F. Genet, B. Stephanidis, R. Boursier

cond-mat.supr-conarXiv:cond-mat/0201104

Abstract

We investigate Josephson coupling through a ferromagnetic thin film using Superconductor-Insulator-Ferromagnet-Superconductor planar junctions. Damped oscillations of the critical current are observed as a function of the ferromagnetic layer thickness. We show that they result from the exchange energy gained or lost by a quasiparticle Andreev-reflected at the ferromagnet-superconductor interface. The critical current cancels out at the transition from positive ("0") to negative ("π") coupling, in agreement with theoretical calculations.

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